Can you see any marks that could be from a sting or tick bite? Those may cause sudden swelling of the face or the comb. It looks like both sides of her face are slightly swollen, as well as the comb. I suppose if she slept all night with her head down, as some chickens will occasionally do, the swelling could spread to the comb.
I would look for marks or stings, a tick, and give her 1/2 of a 25mg bendryl tablet only once, to see if the swelling decreases. But continue the Tylan for at least 3 days, since you started it.